A technology has been developed for detecting leak of hydrogen gas, which is a fuel gas, in the conventional fuel cell systems. For example, as described in Japanese Patent Application Laid-open No. 2002-151126, a pressure of a hydrogen tank is detected to detect an amount of hydrogen gas used, the current amount of hydrogen gas used is estimated from the past driving history, and gas leak is detected based on the detected amount of hydrogen gas used and the estimated amount of hydrogen gas used.
Japanese Patent Application Laid-open No. 2003-308868 disclosed an invention according to which a pressure drop ratio is calculated based on an elapsed time and pressure information from a pressure sensor after closing a shutdown valve, and the shutdown valve is considered to be in a damaged state when the pressure drop ratio is less than a predetermined threshold value.